Attaching images: yeah, the first few post will have to be manually approved before the forum allows posting images and/or attachments.
In this case it worked 😁
Ouch, sounds like one of those random and not very useful messages.
Common mistake, which I doubt it will be, would be the wrong path (eg. local path versus share path).
But I'm confident you already checked that.
Next guess would be SMB protocol version (dialect) ...
A while ago this would be rather common with older NAS devices.
Add the "vers=x.y" option to your mount, something like this:
mount -t cifs //servername/someshare -o vers=3.0 /mnt/tmp
Default I believe SMB will try to go with version 2 or better. However, for example a version 1 mount to a version 3 server would fail.
Version 1 is the classic SMB protocol and version 3.x is currently the "common" SMB protocol. There are some changes in for example password encryption and such.
You could explore the "sec" parameter (security) - maybe give "sec=ntlmv2" a try as an option in your mount.
Are you seeing any errors elsewhere (RPi and laptop) ? (dmesg on either machine)
All this is kind-a odd, since it worked before. I think we can agree that it must be a config issue on the newly install Raspberry OS ...